1. Technical Field
The present invention relates to a brushed motor in which an armature including a core with windings wound thereon is disposed on a rotary shaft, the armature being electrically fed by means of brushes slidably engaged with a commutator on the rotary shaft.
2. Description of the Related Art
A brushed motor of this type includes a stator and a rotor which are disposed in a housing. The stator includes a field magnet fixed on an inner peripheral surface of the housing. The rotor includes an armature disposed on a rotary shaft rotatably supported in the housing. The armature has a core with windings for respective poles wound thereon. The windings for the poles are electrically connected to a commutator. The commutator has an outer peripheral surface with which brushes are slidably engaged to supply power to the armature. The direction of electric current flowing through the windings is successively reversed to vary the magnetic fields between the windings and the field magnet, thereby rotating the rotor.
Small, inexpensive, and high-efficiency brushed permanent magnet motors are being widely used for various applications. However, the structure in which the brushes are slidably engaged with the outer peripheral surface of the commutator, and in which the rotor having the windings disposed in the grooves between salient poles of the core is rotated leaves room for improvement in terms of quietness during operation. Accordingly, various proposals have been made.
For example, JP-A-2001-309615 discloses a brushed motor in which a brush holder made of sheet metal for holding the brushes is formed with reinforcement ribs and has a two-fold double structure for increased stiffness. In this way, vibrations at the distal end of the brushes when slidably engaged with the commutator are suppressed to reduce noise.
JP-A-2006-211758 discloses a brushed motor in which a vibrator is configured by fixing, via an elastic body, a substantially dice-shaped weight to the distal end of a brush holder for holding a brush. Vibrations caused in the brush holder are transmitted to the weight and dissipated in the form of vibration energy, thereby reducing the vibration of the brush holder and hence noise.